Evaluating Autoxidation Radical Scavengers and Additives to Enhance Aminopolymer Sorbent Stability

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• Solid amine sorbents are promising for removing atmospheric carbon dioxide (CO2).
• These sorbents degrade due to oxidation from environmental factors like O2 and H2O.
• Amine oxidation is a major challenge limiting sorbent longevity in direct air capture (DAC).

Purpose of the Study:

• To investigate radical scavengers and additives for mitigating degradation in poly-(ethylenimine) (PEI)/Al2O3 sorbents.
• To evaluate the effectiveness of 4,4'-bis-(α,α-dimethylbenzyl)-diphenylamine (BDDPA) as a stabilizer.
• To assess sorbent stability under various direct air capture (DAC)-relevant conditions.

Main Methods:

• Incorporation of BDDPA into a model PEI/Al2O3 sorbent.
• Exposure of sorbents to CO2-free air (21% O2/N2) at 120 °C.
• Testing under humid (43% RH) and dry air with and without 0.04% CO2 at 70 °C and 120 °C.

Main Results:

• BDDPA-incorporated PEI/Al2O3 sorbents demonstrated superior resistance to oxidative degradation.
• Enhanced stability was observed under dry and humid conditions, with and without CO2, at elevated temperatures.
• BDDPA significantly improved sorbent stability compared to the pristine material, even under humid, CO2-free air.

Conclusions:

• BDDPA is an effective antioxidant for stabilizing PEI/Al2O3 sorbents against degradation.
• The findings highlight the importance of testing sorbents under realistic DAC conditions, including humidity and CO2.
• BDDPA shows promise for prolonging sorbent lifespan, advancing direct air capture technologies.